The goal of this research is to develop a "mega-PCR" procedure in which DNA between two DNA sequences hundreds of thousands or even millions of base pairs apart can be amplified enzymatically and directly cloned from the amplification reaction. If this procedure can be developed, it could be coupled with sequence tagged sites (STSs) to greatly simplify major aspects of the human genome project. Thus, it would be possible to make mega-PCR primers from any two STSs within, perhaps, one million base pairs of each other and use these to amplify the intervening DNA. It would be unnecessary to clone the genome, since any region flanked by STSs could be amplified at will for study. If PCR amplification of million base pair regions of DNA is successful, the number of STSs required to cover the genome would be reduced by up to a factor of 10. It would be possible to amplify inserts from yeast artificial chromosomes or cosmids for a variety of purposes. Mega-PCR would greatly facilitate cloning of interesting disease genes because all that would be required would be two flanking markers within the amplifiable distance to clone the gene. Thus, mega-PCR would significantly aid many aspects of the human genome initiative.